Utility vehicles for use in the agricultural, lawn and golf course maintenance fields typically travel directly upon the turf surface being maintained. Such vehicles must often support a substantial weight (greater than one ton) on a frame having a relatively short wheelbase. Inherent in such applications is the need to travel over uneven terrain, freshly watered grass or recently planted soil. Obstacles such as shrubbery, sand traps and trees are also often encountered.
Utility vehicles of this type are often used to apply fertilizer, pesticides or other surface treatments to the turf being maintained. In order to provide complete ground coverage, the vehicle must approach as closely as possible the various obstacles, such as trees and fences, which are often present in such areas. This requires that the turning radius of such a vehicle be as small as possible.
In order to prevent damage to the turf and to promote safety while traveling in off road environments, the maximum speed of many utility vehicles is limited to approximately twenty miles per hour. Unfortunately, this encourages the tendency to drive at maximum speed under most conditions, including during maximum steering wheel deflection turns. Since scuffing of the turf or soil is unacceptable, each wheel must follow a coordinated, non-skid path regardless of vehicle speed, terrain conditions or radius of turn.
Unfortunately, past utility vehicles have not provided a complete solution to these various problems. For example, maximum wheel deflection has been limited to approximately forty-five degrees to ensure proper tracking along an ideal "Ackerman" arc. Attempts to provide greater maximum deflection have required solutions too complex for use in utility vehicle applications.
Similarly, the great weight carried by such vehicles while traveling over uneven terrain has necessitated the implementation of substantial shock absorption capability at each axle. Conventional methods have utilized a substantially vertically oriented spring, or other damping device, mounted between the wheel support structure and the vehicle frame. The effect of such an arrangement, however, is a tendency, for example, to lift the rear wheel of the vehicle when the front wheel encounters a bump or mogul requiring significant vertical displacement of the wheel. This results in reduced traction of the rear wheel which resides on the same side of the vehicle as the displaced front wheel.
In an effort to overcome the aforementioned problems, various solutions involving horizontally mounted springs or shock absorbers have been proposed. For example, U.S. Pat. No. 3,292,945, issued to Dangauthier, discloses a "damping collecting means" including two tubular telescoping elements having ends pivotably attached, through various linkages, to the wheel supports. When the wheels are deflected upwardly by an impulse load, the "damping connecting means" (shock absorber) is compressed and applies a reaction force to the wheel tending to urge the wheel downwardly so as to maintain (or reestablish) ground contact. A similar device is also disclosed in U.S. Pat. No. 4,740,013, issued to Pierce, Jr., which differs from Dangauthier primarily in the rigid attachment of the shock absorber housing to the vehicle frame. Both of the aforementioned devices suffer from the drawback of requiring a relatively sophisticated dampening element, including a housing, O-rings, biasing springs, return springs, pistons and hydraulic fluid, as well as periodic maintenance and replacement.
In a utility vehicle of the type contemplated herein, the designer, manufacturer and end user would much prefer to utilize a simpler dampening element, such as a spring, while maintaining the desired horizontal orientation. An effort to employ a horizontally oriented spring in a shock absorption function is disclosed, for example, in U.S. Pat. No. 3,747,950, issued to Hager. The Hager device utilizes a spring confined between two end plates, but suffers from the problem of spring "buckling", which occurs when the end plates assume a non-parallel configuration. The non-parallel end plate orientation is a heretofore inevitable result of relative movement between the wheel support and vehicle frame which occurs whenever an impulse load is applied to the wheel. This buckled condition causes the shock absorption effectiveness of the spring to be diminished, and necessitates the use of centering and retaining members within the spring (such as disclosed by Hager) in order to prevent the spring from being completely ejected from its end plate cradle.